This invention relates generally to fire alarm systems, and more particularly, to methods and apparatus for indicating power conditions at notification appliances installed within fire alarm systems.
In general, alarm systems include several notification appliances that are joined to common power lines extending from a system controller. The power lines experience a voltage drop along the lines due to line resistance.
Notification appliances have one or more alarm indicators (i.e. strobes and horns) to notify people in the area of an alarm condition. Notification appliances include various electronic components that have certain power requirements. The notification appliances are generally powered by a remote power supply located, for example, in the system controller or some other remote site. Each notification appliance has a power operating range within which the device operates to provide the appropriate alarm indicators. A predefined or predetermined power (e.g., voltage and current) operating range may be set by a manufacturer or a regulatory body such as Underwriters Laboratories (UL). Different types of notification devices may have different voltage and/or current operating ranges.
Prior to installation, voltage drop calculations are obtained for the alarm system. The voltage drop calculations may be based on blueprints or other plans of the layout of the building and a lump sum calculation of voltage drop. However, the actual wire distances installed are typically different than as estimated, as the wire is run based on the actual physical building layout and obstacles. Therefore, estimating practices using the lump sum method of calculating voltage drops also add a margin of safety to the calculation. However, the margin of safety does not guarantee that the installed appliances are within the estimated distances of the system controller.
Therefore, after notification appliances are installed in a fire or other alarm system, the power, signal and/or voltage level at each of the notification appliances is verified to assure that the level of interest is within the desired range for operation. The verification is obtained by manually testing with a test meter a notification appliance circuit at each of the notification appliances. If the voltage level is outside the range (i.e. too high or too low) the notification appliance may not operate properly. Voltage that is below the operating range of the notification appliance can cause the appliance to produce visible signal intensities or sound pressure levels that are below the levels of the designed system. Also, voltage that is outside of the designed operating range may damage components, leading to premature failure. Depending upon the number of notification appliances installed, this manual testing process can be time consuming and adds significant labor cost to an installation. The voltage verification can also be disruptive, especially in buildings such as hospitals which do not typically have an unoccupied period during which testing can be performed.
In addition to testing the system upon installation, the system may need to be tested periodically, such as annually or semi-annually depending upon prevailing fire code and regulations, and the type of system and/or appliances and devices installed. System overloading may also occur after a system has been installed if devices are added to the system without verifying the system load capacity. This may cause the system to not function properly or experience premature failure as discussed above. Also, if the system is overloaded and already operating at a lower voltage level, the appliances may not operate as designed when the incoming AC power nears a brownout condition or after operating on battery power for a length of time.
Therefore, a need exists for an improved way to verify the power, signal and/or voltage levels at each notification device after installation and during an inspection. Additionally, a need exists for an improved way to verify that a system has not been overloaded by additional devices. Certain embodiments of the present invention are intended to meet these needs and other objectives that will become apparent from the description and drawings set forth below.